1. Field of the Invention
The present invention relates to a microstrip transmission line device, and particularly to a microstrip transmission line device for use in a power distribution/synthesis circuit having a resistor part and a method for manufacturing the microstrip transmission line device.
2. Description of the Related Art
In a microwave circuit such as a Wilkinson circuit used for power distribution/synthesis, a resistor is required at a predetermined position on a line. There is a case that a resistor has to be inserted between a transmission line and a ground in order to prevent oscillation in a microwave circuit (for example, see Jpn. Pat. Appln. Laid-Open Publication No. 11-330813).
If a microwave circuit requires a resistor as described above, the resistor is conventionally formed through process described below. That is, as shown in FIGS. 1 and 2, a resistance layer 3 (FIG. 2) is accumulated on an entire face of an insulating layer 2 (FIG. 2) such as ceramic substrate having a back face provided with a ground layer 1 (FIG. 2). A metal conductive layer 4 is accumulated on the resistance layer 3.
Next, as shown in FIGS. 3 and 4, a part of the metal conductive layer 4 provided on the resistance layer 3 is removed by etching or the like. Further, as shown in FIGS. 5 and 6, an unnecessary region is removed from the resistance layer 3. At this time, a necessary region of the resistance layer 3 is left intact, thereby forming a resistor 5.
Paying attention to a conductive region 7 thus formed, the region 7 (FIG. 5) has a structure as shown in FIG. 7. That is, as a microstrip line, an electromagnetic wave is generated between the ground layer 1 provided on a back face of the insulating layer 2 and the metal conductive layer 4, allowing a line of electric force 8 to pass through the resistance layer 3.
If the operating frequency is low, existence of the resistance layer 3 provided under the metal conductive layer 4 does not substantially cause any serious problem. However, if the operating frequency is so high like in case of a microwave, the resistance layer 3 under the metal conductive layer 4 has a rather larger electric power distribution than the metal conductive layer 4, causing transmission loss to increase in the resistance layer 3.